Floating Action Button with square shape

Question

When I set a color to my fab, it looks like so:

My layout xml:

Answer 1

Use

app:backgroundTint="@android:color/holo_green_dark"

(for example) to set color of fab. Result below. Taken from this -tested- code snippet.

Also edit : "strange green color" should come from your accent color. That's the color fab takes by default.